J
Jeroni Paul
- Jan 1, 1970
- 0
Hi,
This is a 100Hz wide screen TV.
I've just repaired this TV after a general blowup of many parts due to the
supply not properly regulating, now all works fine.
However I appreciate in dark scenes that brighting objects are too bright,
defocus and get trailing lines to the right as in the point of beginning an
avalanche. If the same object remains but the average brightness increases,
the problem goes away, this is because the average beam current limiter
operates. This points to the peak beam current limiter not operating,
however I've carefully studied its schematics and I see no peak limiter
anywhere.
The RGB output is a TDA4780, it receives cathode current information from
the three cathode drivers TDA6111Q. It is entered on pin 19, which is used
to adjust the automatic cut-off point and leakage measurement. In pin 15 it
receives the flyback HV return that is used for average limiting, a 10uF
capacitor is connected which filters out any peak. That's all, no peak
limiting anywhere. Any idea what I'm missing?
In TDA4780 datasheet appears a block called peak limiter absolute, but it
takes its own RGB signals, no external beam current info.
BTW the G2 and RGB adjustments might be messed by someone before, a partial
fix is to lower RGB drive values in service menu to eliminate that effect at
max contrast, but I'd hope some sort of peak limiter should exist in an
expensive set like this.
Thank you.
This is a 100Hz wide screen TV.
I've just repaired this TV after a general blowup of many parts due to the
supply not properly regulating, now all works fine.
However I appreciate in dark scenes that brighting objects are too bright,
defocus and get trailing lines to the right as in the point of beginning an
avalanche. If the same object remains but the average brightness increases,
the problem goes away, this is because the average beam current limiter
operates. This points to the peak beam current limiter not operating,
however I've carefully studied its schematics and I see no peak limiter
anywhere.
The RGB output is a TDA4780, it receives cathode current information from
the three cathode drivers TDA6111Q. It is entered on pin 19, which is used
to adjust the automatic cut-off point and leakage measurement. In pin 15 it
receives the flyback HV return that is used for average limiting, a 10uF
capacitor is connected which filters out any peak. That's all, no peak
limiting anywhere. Any idea what I'm missing?
In TDA4780 datasheet appears a block called peak limiter absolute, but it
takes its own RGB signals, no external beam current info.
BTW the G2 and RGB adjustments might be messed by someone before, a partial
fix is to lower RGB drive values in service menu to eliminate that effect at
max contrast, but I'd hope some sort of peak limiter should exist in an
expensive set like this.
Thank you.
